Variable displacement pump

Abstract

Discharge port ( 26 ) as arc-recessed discharge portion is formed by cutting on bottom surface ( 13 a ) of pump accommodating portion ( 13 ) of variable displacement pump. On mounting surface ( 1 b ) of housing body ( 1 ), first low pressure chamber ( 281 ) is formed at position overlapping with discharge port ( 26 ) in radial direction of pump structure ( 14 ) formed by driving shaft ( 3 ), rotor ( 4 ) and vanes ( 5 ) Drain hole ( 28 b ) communicating with low pressure portion located outside housing body ( 1 ) is formed on bottom surface ( 28 a ) of first low pressure chamber ( 281 ) along direction of rotation axis (O 1 ) of pump structure ( 14 ). Low pressure portion has pressure that is hydraulic pressure of oil discharged from discharge port ( 26 ) or less. Oil from discharge port ( 26 ), having higher pressure than first low pressure chamber ( 281 ), flows into first low pressure chamber ( 281 ) by pressure difference between discharge port ( 26 ) and first low pressure chamber ( 281 ).

The invention claimed is: 
     
         1 . A variable displacement pump comprising:
 a pump housing having a pump accommodating portion, a suction portion and a discharge portion wherein the suction portion and the discharge portion are open at the pump accommodating portion;   an adjustment ring movably provided in the pump accommodating portion;   a pump structure provided inside the adjustment ring and discharging oil, which is sucked from the suction portion, from the discharge portion by being driven and rotated, wherein a flow amount of the oil discharged from the discharge portion by the pump structure is changed when the adjustment ring moves;   a control hydraulic chamber provided between the pump accommodating portion and the adjustment ring in a radial direction of the pump structure with respect to a rotation axis of the pump structure and forcing the adjustment ring in a direction in which the flow amount of the oil discharged from the discharge portion decreases when a control pressure is introduced into the control hydraulic chamber;   a control valve controlling pressure of oil in the control hydraulic chamber; and   a first low pressure chamber provided at a position that overlaps with the discharge portion between the pump accommodating portion and the adjustment ring in the radial direction of the pump structure with respect to the rotation axis of the pump structure and always communicating with an oil pan having atmospheric pressure that is equal to or less than a hydraulic pressure of the oil discharged from the discharge portion,   wherein the first low pressure chamber is provided with a drain hole that directly communicates with the oil pan, and   wherein the first low pressure chamber is configured such that the atmospheric pressure of the oil pan is introduced into the first low pressure chamber through the drain hole, and the oil discharged from the discharge portion flows into, through a gap between the adjustment ring and the pump housing, the first low pressure chamber by a pressure difference between the discharge portion and the low pressure chamber, and the oil flowing into the first low pressure chamber is drained to the oil pan through the drain hole.   
     
     
         2 . The variable displacement pump as claimed in  claim 1 , wherein:
 the pump accommodating portion has a pivot portion provided so as to be adjacent to the first low pressure chamber in a rotation direction of the pump structure, and   the adjustment ring pivots on the pivot portion.